‘Big Farmer' firms plan pesticides to manipulate gene expression

Spray away? Pesticides that work by tinkering with gene expression in the pest without modifying crop genes could get around regulations on genetic modification. The technology is based on a process called RNA interference and may be ready within the next five years.

In June, researchers at Cornell University in Ithaca, New York, showed that an RNA spray can kill the Colorado potato beetle, protecting potato plants for more than 28 days.

“This is a technology that could allow the development of a whole new generation of agrichemicals,” says David Baulcombe of the University of Cambridge.

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Industry is taking notice. Monsanto hopes to have an RNA spray ready by 2020 that will tackle potato beetles resistant to many other types of pesticide.

Because this approach silences genes but does not introduce heritable changes into the genome, it may not be regulated as a GM product. “In effect these are chemical pesticides, they just happen to be RNA,” says Baulcombe.

Silencing genes

The approach is based on RNA interference (RNAi), a protective mechanism that occurs naturally in cells. The process has evolved to detect the double-stranded RNA produced by viruses, but can be repurposed to silence any gene. One way to do this is to use short sequences of double-stranded RNA to trigger enzymes in the cell to stop any proteins being made that correspond to its sequence.

In the past, crops have been genetically modified to produce RNA molecules that protect the plant by triggering RNAi in the insects that eat them – but GM crops are less likely to be approved and used, particularly in Europe.

Researchers are now developing RNA sprays for crops instead.

Targeted toxin

One advantage touted for this technology is that it would allow farmers to target pests more specifically. Chemical pesticides, for example neonicotinoids, can harm other species.

By using sequences of RNA that match specific gene sequences in a pest, RNAi should leave other species unscathed.

In practice this could be difficult. To kill an insect, the RNAs must silence a gene essential for life, and species often share genes of such crucial importance, making it difficult to target one insect over another.

The Cornell study targeted the Colorado potato beetle’s gene for actin, a structural protein common across all complex life forms. In their paper, the researchers suggest that actin might not be an ideal target for crop protection, for this reason – the house fly’s actin gene is 80 per cent identical to the beetle’s, for example.

“They need to find another gene in the insect that is essential for it but not in other organisms,” says Saskia Hogenhout of the John Innes Centre in Norwich, UK.

Spray safe?

Another concern is that bacteria might absorb the sprayed RNAs and use them. “Bacteria can take up nucleic acids,” says Jones. But he says this would only be a potential hazard if the RNAs provided them with a selective advantage. “This would be highly unlikely in the case of RNAi.”

Another worry is that a sequence used to kill an insect might, by chance, also match an important sequence in humans. “That can be tested,” says Hogenhout.

“With all technologies, there’s always a risk,” says Hogenhout. “My opinion is the RNAi approach would be a better option than pesticides that are less specific.”

An increasing number of pesticides are being banned for their unspecific effects. “If you talk to farmers, particularly in northern Europe, they’re very concerned about the limited range of crop protection chemicals that they have available to them because of concerns about the broader environmental effects,” says Baulcombe.

For example, he says, it would be “wonderful” if a specific RNAi treatment that doesn’t harm bees were able to replace neonicotinoids.